The present invention relates to an organic photosensitive member excellent in antioxidation, in particular ozone resistance.
Recently, a large number of organic photosensitive members have been proposed and practically used as electrophotographic sensitive members.
However, the organic photosensitive members are low in surface hardness, so that in the case where they are practically used inside an electrophotographic machine, the photosensitive layer is worn by the contact with developer, transfer paper, cleaning member and the like and thus the layer-thickness of the photosensitive layer is reduced after the long-term use and the surface potential is reduced, whereby the sufficient image concentration can not be obtained.
In addition, in an electrophotographic machine with the mechanism for compulsorily maintaining the surface potential of the photosensitive member constant by, for example, changing an output of the charger with monitoring by means of the surface potentiometer and charging by the scorotron method incorporated therein, it becomes necessary as the surface thickness decreases that the charging quantity to be applied to the surface is increased to maintain the surface potential constant, so that the sensitivity is lowered and the foggy image is generated after the long-term use.
So, in order to improve the wear resistance of the organic photosensitive member, a large number of proposals of forming a surface protective layer on the outermost surface have been made. Such a surface protective layer is generally formed on the photosensitive layer in a layer-thickness of about several .mu.m or less so that the residual potential may not be generated and the irradiation ray may be effectively introduced into the photosensitive layer not to lead to the reduction of the sensitivity.
However, the surface of the photosensitive member in the practical electrophotographic machine is damaged by the corona discharge from various kinds of charger aiming at the provision of the surface charge, the transfer of the developer, the separation of the transfer paper from the photosensitive member and the like.
The damages by charging include ionic damages by corona ions, ozone damages by the ozone gas generated by the corona discharge and the like, which influence adversely much upon the performances of the photosensitive member.
This adverse influence is explained as follows with reference to the constitution of the photosensitive member, which has been generally adopted and composed of a charge generating layer and a charge transporting layer formed on an electrically conductive substrate in this order.
The ozone gas itself is strong in oxidizing effect enough to deteriorate a charge transporting material in the charge transporting layer.
The concentration of the ozone gas inside the usual electrophotographic machine is about 1 ppm or less. But, as the photosensitive member is exposed to the ozone atmosphere repeatedly for a long time, the charge transporting material is oxidized gradually from the outermost surface to form a so-called ozone-deteriorated region.
The charge transporting layer generally has the remarkably porous constitution at a molecular level due to the existence of so-called byways of solvents formed by the evaporation of the solvents in the preparation, the physical impact destruction resulting from the collision of ions when charged and the like, so that it is remarkably permeable to ozone. According to the present inventors' knowledges, this ozone-deteriorated region generally reaches about 5 .mu.m under the surface protective layer after the long-term use.
In the organic photosensitive member which has not a surface protective layer, the ozone-deteriorated region is worn out adequately by contact with a member brought into contact with the photosensitive member, so that it may show a disadvantage resulting from the wear of the photosensitive layer but no bad influence resulting from the ozone-deteriorated layer occurs.
However, because the organic photosensitive member with the surface protective layer is not worn, the ozone-deteriorated region is not removed but gradually formed and also its region is expanded.
If the surface protective layer is so chemically stable and so dense that the intrusion of ozone can be perfectly prevented, the ozone-deteriorated layer must not be formed. But such the dense surface protective layer can not be substantially prepared. Moreover the surface protective layer is damaged by oxidizing effects of ozone, physical destructions by ion-impacts or the like. Therefore, ozone molecules reach the photosensitive layer through the surface protective layer.
In the ozone-deteriorated region, the mobility of carriers is reduced and the carriers, which are moving, are trapped, so that the sensitivity is reduced and the residual potential is increased.
In addition, the trapped carriers are recombined with the surface charges when recharged to lead to the reduction of the surface potential.
Furthermore, when the photosensitive member, in which the ozone-deteriorated region is formed, is installed in the electrophotographic machine to be used under the high-temperature and high-humidity conditions, the moisture in the atmosphere reaches the ozone-deteriorated layer to be absorbed, whereby an electric resistance is reduced remarkably to generate the so-called image flow.
The invention aiming at the prevention of the ozone-deterioration has been disclosed in, for example, Japanese Patent Application Laid-Open No. 59-135477 or Japanese Patent Application Laid-Open No. 59-136744.
Japanese Patent Application Laid-Open No. 59-135477 discloses a photosensitive member of binder type containing phthalocyanines in which antioxidants or mixtures thereof with synthetic waxes are applied to an outer surface of said photosensitive member.
It is, however, produced by the applying method, so that if it is practically used inside a copying machine, the antioxidants and the like applied onto the surface of the photosensitive member are removed by the contact with the developer, the transfer paper, the cleaning member and the like to become short of the stability of the photosensitive member. Its durability with respect to copy is at most about several thousand times of copy.
Japanese Patent Application Laid-Open No. 59-136744 discloses a photosensitive member comprising a photosensitive layer with photoconductive powders dispersed in binder resins and an insulating protective layer containing antioxidants formed on said photosensitive layer.
Contrary to the present invention characterized in that antioxidants are contained in a charge transporting layer, antioxidants are contained in the surface protective layer in the above described invention. In addition, in order to achieve the sufficient resistance to oxidation, it is necessary to increase a layer-thickness of the insulating protective layer. In this case, the residual potential is apt to be generated.
Furthermore, this invention can not be applied to insulating protective layers to which antioxidants can not be added in view of the preparation method.
The inventions paying attention to the charge transporting material in order to prevent the ozone-deterioration have been disclosed in, for example, Japanese Patent Application Laid-Open Nos. 63-63046, 59-155844, 59-155845, 58-62654 and the like.
Japanese Patent Application Laid-Open No. 63-63046 discloses a laminate type photosensitive member comprising a substrate and a charge generating layer and a charge transporting layer formed on said substrate, wherein the concentration of the charge transporting material contained in the charge transporting layer is continuously changed. The charge transporting material is contained in an more increased quantity in the direction to the substrate. Thus, the insulating property and the hardness in the vicinity of the surface are improved and additionally the charge transporting material is prevented from depositing on the surface.
In the present invention, the charge transporting material is contained more in the direction to the surface to prevent the ozone-deterioration of the charge transporting material in the vicinity of the surface and secure the suitable transportability even after the long-term use. Accordingly, the present invention is completely different from the above described invention.
Japanese Patent Application Laid-Open Nos. 59-155844 and 59-155845 disclose a laminate type electrophotographic photosensitive member, characterized in that a layer composed of organic acceptor materials and a layer with donor materials of low molecular weight dispersed in resins are formed on an electrically conductive substrate to form a thin layer of charge-transfer complex on an interface therebetween. However, the above described invention relates to a method for preventing the charge transfer through the interface in the laminated type photosensitive layer and does not suggest the prevention of the deterioration in ozone resistance at all.
Japanese Patent Application Laid-Open No. 58-62654 discloses a photosensitive member with charge transporting materials ununiformly dispersed in a charge transporting layer. However, the charge transporting materials are not contained under the condition that they are distributed at the specified concentration and it is an object of Japanese Patent Application to improve the sensitivity. The ozone resistance is not suggested at all.